SLI Option not working

I've got two 1080Ti's in SLI and although I have enabled the SLI option ingame I am not seeing any use from my second card. The first is at 100% utilisation and the second is at 4% which gives me an average framerate of 45 FPS at 4K when in the command ship. In game I'm getting around 80FPS+ on some maps but that's still with only a single graphics card.